Algorithms and Software for Meteor Detection

An ever increasing variety of electronic instrumentation is being brought to bear in meteor studies and analysis, with unique meteor detection challenges arising from the attempt to do automated and near real-time processing of the imagery. Recent algorithm developments in the literature have been applied and implemented in software to provide reliable meteor detection in all-sky imagers, wide-field intensified video, and narrow field-of-view telescopic systems. The algorithms that have been employed for meteor streak detection include Hough transforms with phase coded disk, localized Hough transforms with matched filtering, and fast moving cluster detection. They have found application in identifying meteor tracks in the Spanish Fireball Network all-sky images, detailed analysis of video recordings during the recent Leonid meteor storms, and development of a detection/cueing technology system for rapid slew and tracking of meteors.     

The Canadian Meteor Orbit Radar Meteor Stream Catalogue

The Canadian Meteor Orbit Radar is a multi-frequency backscatter radar which has been in routine operation since 1999, with an orbit measurement capability since 2002. In total, CMOR has measured over 2 million orbits of meteoroids with masses greater than 10 μg, while recording more than 18 million meteor echoes in total. We have applied a two stage comparative technique for identifying meteor streams in this dataset by making use of clustering in radiants and velocities without employing orbital element comparisons directly. From the large dataset of single station echoes, combined radiant activity maps have been constructed by binning and then stacking each years data per degree of solar longitude. Using the single-station mapping technique described in Jones and Jones (Mon Not R Astron Soc 367:1050–1056, 2006) we have identified probable streams from these single station observations. Additionally, using individual radiant and velocity data from the multi-station velocity determination routines, we have utilized a wavelet search algorithm in radiant and velocity space to construct a list of probable streams. These two lists were then compared and only streams detected by both techniques, on multiple frequencies and in multiple years were assigned stream status. From this analysis we have identified 45 annual minor and major streams with high reliability.     

近20年来狮子座流星雨预报进展

对近20年来狮子座流星雨的预报工作，进行了系统的阐述和分析。1998年Tempel-Tuttle彗星的回归，再度带来了狮子座流星雨的观测热，也大大促进了对狮子座流星雨预报工作的研究与验证。有的研究在时间预报准确度方面已显示出其模型的优越性，有的在流星雨的强度方面显示出一定的准确度。指出了两大类不同的方法实际上是在三维空间强调了不同的方面。将不同方法的优势结合起来，可能会使流星雨的预报更加成熟。     

流星雨摄影观测记录的罕见现象

2001年狮子座流星雨,是几百年来难得有机会在中国观测到的一场流星暴。在我们收集到的照相观测资料中,发现了一些特殊的、还未引起广泛注意的流星现象。"蛇行"的流星以及螺旋形并带有辐条结构的流星余迹,早在我国古代记录中就可以找到印证。现代的照相技术,不仅直观地显示了文字难以描述的颜色、形态和变化,而且提供了可永久性进行测量的记录。其中包括罕见的对流星余迹的双站观测资料。用常规的"高空风作用"难以解释这些观测现象。它们可能反映了流星带电体与地球磁场的相互作用。     

The IAU Meteor Shower Nomenclature Rules

The International Astronomical Union at its 2006 General Assembly in Prague has adopted a set of rules for meteor shower nomenclature, a working list with designated names (with IAU numbers and three-letter codes), and established a Task Group for Meteor Shower Nomenclature in Commission 22 (Meteors and Interplanetary Dust) to help define which meteor showers exist from well defined groups of meteoroids from a single parent body.     

Meteor Outburst Profiles and Cometary Ejection Models

The spatial structure of meteor streams, and the activity profiles of their corresponding meteor showers, depend firstly on the distribution of meteoroid orbits soon after ejection from the parent comet nucleus, and secondly on the subsequent dynamical evolution. The latter increases in importance as more time elapses. For younger structures within streams, notably the dust trails that cause sharp meteor outbursts, it is the cometary ejection model (meteoroid production rate as a function of time through the several months of the comet’s perihelion return, and velocity distribution of the meteoroids released) that primarily determines the shape and width of the trail structure. This paper describes how a trail cross section can be calculated once an ejection model has been assumed. Such calculations, if made for a range of ejection model parameters and compared with observed parameters of storms and outbursts, can be used to constrain quantitatively the process of meteoroid ejection from the nucleus, including the mass distribution of ejected meteoroids.     

Meteor Orbit Determinations with Multistatic Receivers Using the MU Radar

The MU radar of RISH (Research Institute for Sustainable Humanosphere, Kyoto University), which is a MST radar (46.5 MHz, 1 MW peak power), has been successfully applied to meteor studies by using its very high versatility. The system has recently renewed with 25 channel digital receivers which significantly improved the sensitivity and precision of interferometer used in meteor observation. The transmission is now synchronized to GPS signals, and two external receiving sites with a ranging capability has additionally been operated in order to determine the trajectories and speeds of meteoroids.     

The Armagh Observatory Meteor Camera Cluster: Overview and Status

Armagh Observatory installed a sky monitoring system consisting of two wide angle (90° × 52°) and one medium angle (52° × 35°) cameras in July 2005. The medium angle camera is part of a double station setup with a similar camera in Bangor, ∼73 km ENE of Armagh. All cameras use UFOCapture to record meteors automatically; software for off-line photometry, astrometry and double station calculations is currently being developed. The specifications of the cameras and cluster configuration are described in detail. 2425 single station meteors (1167, 861 and 806 by the medium-angle and the wide-angle cameras respectively) and 547 double station meteors were recorded during the months July 2005 to Dec 2006. About 212 double station meteors were recorded by more than one camera in the cluster. The effects of weather conditions on camera productivity are discussed. The distribution of single and double station meteor counts observed for the years 2005 and 2006 and calibrated for weather conditions are presented.     

TV Meteor Observations from Modra

We present our experience and initial results of single-station observation using the new fish-eye TV system, as well as double station TV observation of the Geminids 2006 shower. The fixed fish-eye TV system was developed for monitoring meteor activity throughout the year. We discuss the astrometric precision of our observations using the UFOAnalyser software.     

Multicolor Photometry for Mode Identification

The goal of asteroseismology is to discern the physical conditions of stars by comparing observed pulsations with models.To obtain this goal, the observed pulsation periods and the spherical harmonics (n, , and m) need to match the theoretical model.Typically the most difficult part in this process is the identification of the pulsation modes in the observations.Multicolour photometry is one method that has proven useful for identifying pulsation modes.By observing stars through various wavebands, and comparing the amplitudes and phases, it is possible to determine the spherical harmonics.This contribution will emphasize the work of Watson (1988), which has since been applied to many different types of variable stars including Scuti (Garrido et al., 1990), Doradus (Breger et al., 1997), Cepheid (Cugier et al., 1994), and EC 14026 (Koen, 1998) stars. I will also discuss the technique of summing spectra (especially UV) into various wavebands which are then used to identify modes as pioneered by Robinson, Kepler, and Nather (1982) and applied to white dwarf stars (Kepler et al., 2000).     

Meteor streams associated with Jupiter family comets

Meteor showers have been observed for a considerable time, and the cause, meteoroids from a meteoroid stream ablating in the Earth's atmosphere, has also been understood for centuries. The connection between meteoroid streams and comets was also established 150 years ago. Since that time our ability both to understand the physics and to numerically model the situation has steadily increased. We will review the current state of knowledge. However, just as there are differences between the behaviour of long period comets, Halley family comets and Jupiter family comets, so also differences exist between the associated meteoroid streams. Streams associated with Jupiter family comets show much more variety in their behaviour, driven by the gravitational perturbations from Jupiter. The more interesting showers associated with Jupiter family comets will be discussed individually.     

Meteor Showers Associated with the Taurid Complex Asteroids

Recent theoretical and observational work has shown that the asteroids belonging to the Taurid meteoroid complex have a cometary nature. If so, then they might possess related meteoroid streams producing meteor showers in the Earth atmosphere. We studied the orbital evolution of ten numbered Taurid complex asteroids by the Halphen-Goryachev method. It turned out that all of these asteroids are quadruple crossers relative to the Earth's orbit. Therefore their proposed meteoroid streams may in theory each produce four meteor showers. The theoretical orbital elements and geocentric radiants of these showers are determined and compared with the available observational data. The existence of the predicted forty meteor showers of the ten Taurid complex asteroids is confirmed by a search of the published catalogues of observed meteor shower radiants and orbits, and of the archives of the IAU Meteor Data Center (Lund). The existence of meteor showers associated with the Taurid Complex Asteroids confirms that, most likely, these asteroids are extinct comets. This revised version was published online in July 2006 with corrections to the Cover Date.     

用陕西天文台流星雷达监测人为空间碎片可能性的分析

本文分析了利用中国科学院陕西天文台的流星雷达进行人为空间碎片监测的可能性．详细计算了到达接收机的回波的信噪比Ｓ／Ｎ依赖于目标散射横截面。和高度距离Ｒ的关系。理论计算表明，利用陕西天文台的流星雷达完全有可能监测在２００ｋｍ至１２００ｋｍ的高度范围内，半径大于０．５ｍ的人为空间碎片．     

Asteroid Models from the Pan-STARRS Photometry

We present simulations on the asteroid photometric data that will be provided by the Pan-STARRS (Panoramic Survey Telescope and Rapid Response System). The simulations were performed using realistic shape and light-scattering models, random orientation of spin axes, and rotation periods in the range 2–24 h. We show that physical models of asteroids can be reconstructed from this data with some limitations (possible multiple pole solutions). We emphasize the potential of sparse photometric data to produce models of a large number of asteroids within the next decade and we outline further tests with fast and slow rotators, tumblers, and binary asteroids.     

Plasma and Electromagnetic Simulations of Meteor Head Echo Radar Reflections

Recently, meteor head echo detections from high powered large aperture radars (HPLA) have brought new measurements to bear on the study of sporadic interplanetary meteors. These same observations have demonstrated an ability to observe smaller meteoroids without some of the geometrical restrictions of specular radar techniques. Yet incorporating data from various radar reflection types and from different radars into a single consistent model has proven challenging. We believe this arises due to poorly understood radio scattering characteristics of the meteor plasma, especially in light of recent work showing that plasma turbulence and instability greatly influences meteor trail properties at every stage of evolution. In order to overcome some of the unknown relationships between meteoroid characteristics (such as mass and velocity) and the resulting head echo radar cross-sections (RCS), we present our results on meteor plasma simulations of head echo plasmas using particle in cell (PIC) ions, which show that electric fields strongly influence early stage meteor plasma evolution, by accelerating ions away from the meteoroid body at speeds as large as several kilometers per second. We also present the results of finite difference time domain electromagnetic simulations (FDTD), which can calculate the radar cross-section of the simulated meteor plasma electron distributions. These simulations have shown that the radar cross-section depends in a complex manner on a number of parameters. In this paper we demonstrate that for a given head echo plasma the RCS as a function of radar frequency peaks at sqrt (2*peak plasma frequency) and then decays linearly on a dB scale with increasing radar frequency. We also demonstrate that for a fixed radar frequency, the RCS increases linearly on a dB scale with increasing head echo plasma frequency. These simulations and resulting characterization of the head echo radar cross-section will both help relate HPLA radar observations to meteoroid properties and aid in determining a particular radar facility’s ability to observe various meteoroid populations.     

流星雷达测距精度的改进

针对目前流星雷达测距误差大的问题，本文提出了提高流星雷达测距精度的新方法，即提高采样速率，用相关分析确定回波脉冲参考点的方法。该方法使流星雷达的测距精度提高一个数量级，测距误差降到±１４ｍ，使流星雷达不仅可以用来观测研究流星，还可用于监测飞机、火箭的飞行等，扩大流星雷达的应用。     

Radio and Meteor Science Outcomes From Comparisons of Meteor Radar Observations at AMISR Poker Flat, Sondrestrom, and Arecibo

Radio science and meteor physics issues regarding meteor “head-echo” observations with high power, large aperture (HPLA) radars, include the frequency and latitude dependency of the observed meteor altitude, speed, and deceleration distributions. We address these issues via the first ever use and analysis of meteor observations from the Poker Flat AMISR (PFISR: 449.3 MHz), Sondrestrom (SRF: 1,290 MHz), and Arecibo (AO: 430 MHz) radars. The PFISR and SRF radars are located near the Arctic Circle while AO is in the tropics. The meteors observed at each radar were detected and analyzed using the same automated FFT periodic micrometeor searching algorithm. Meteor parameters (event altitude, velocity, and deceleration distributions) from all three facilities are compared revealing a clearly defined altitude “ceiling effect” in the 1,290 MHz results relative to the 430/449.3 MHz results. This effect is even more striking in that the Arecibo and PFISR distributions are similar even though the two radars are over 2,000 times different in sensitivity and at very different latitudes, thus providing the first statistical evidence that HPLA meteor radar observations are dominated by the incident wavelength, regardless of the other radar parameters. We also offer insights into the meteoroid fragmentation and “terminal” process.     

Meteors in the IAU Meteor Data Center on Hyperbolic Orbits

The hyperbolic meteor orbits among the 4,581 photographic and 62,906 radar meteors of the IAU MDC have been analysed using statistical methods. It was shown that the vast majority of hyperbolic orbits has been caused by the dispersion of determined velocities. The large proportion of hyperbolic orbits among the known meteor showers strongly suggests the hyperbolicity of the meteors is not real. The number of apparent hyperbolic orbits increases inversely proportional to the difference between the mean heliocentric velocity of meteor shower and the parabolic velocity limit. The number of hyperbolic meteors in the investigated catalogues does not, in any case, represent the number of interstellar meteors in observational data. The apparent hyperbolicity of these orbits is caused by a high spread in velocity determination, shifting a part of the data through the parabolic limit.     

Meteor velocities: A new look at an old problem

Meteoroids that orbit the Sun encounter the Earth with speeds between 11 and 74 km/sec. However, the distribution of the velocities of meteoroids between these limits is not well known. The uncertainty is caused by the difficulty in measuring the true flux of meteors at the extrema of the velocity distribution. Whilst the most comprehensive measurements of meteor flux are those obtained using radio techniques, meteors with speeds > 50 km/sec occur at heights where the effects of initial radius of the trail and diffusion significantly reduce the radio reflection from the trails; on the other hand the high dependence of the collisional ionization probability on velocity (to the power 3.5) significantly inhibits the detection of meteors with speeds < 20 km/sec. Recent developments in meteor radar systems are now making it possible to measure the velocity of meteors at the extrema of the distribution. For meteoroids ablating at heights between 100 and 120 km the speed of entry can be measured at 2 and 6 MHz using a radar with a 1 km diameter array located near Adelaide; these observations will commence early in 1995. In the meantime a 54 MHz MST radar is being operated at a pulse repetition frequency of 1024 Hz to search for the presence of interstellar (speed > 74 km/sec) meteors. Both these radars exploit the phase information available prior to the closest-approach (t_o) point.